Turbine governing system



April 29, 1952 R, SHEPPARD 2,595,007

TURBINE GOVERNING SYSTEM Filed April 25, 1946 2 SHEETS--SHEET l (driven fr'om turbine shan) Inventor: Raym ond S heppard, by His Attorney.

April 29, 1952 R. sHEPPARD 2,595,007

TURBINE GOVERNING SYSTEM Filed April 25, 194e 2 Simms-SHEET 2 :o5 X Tri Z.

.f SYNCHRONZINCI SCREW SETTING o 2o 4'o 5b s'o 7'z 75 ,s'a s :be Tuneme ouTPuT- oF RATED LOAD Inventor: Raymond 5 heppard,

Patented Apr. 29, 1952 TURBINE GOVERNING SYSTEM Raymond Sheppard, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application April 23, 1946, Serial No. y664,266

14 Claims. 1

This invention relates to a governing system` for a prime mover such as a turbine, particularly for a steam turbine adapted to drive a generator delivering electric energy to a network in parallel with a number of other similar turbo-generators. It is particularly adapted for governing such a turbine which is operated over long periods of time at a fixed speed and at an output which may be varied manually, as desired, but is ordinarily substantially constant.

An object of the invention is to provide a governing system for a turbine of the type described which will cause the turbine to operate at a xed output and constant speed, yet which will react quickly in the event of either an increase or drop in speed relative to the established normal speed.

Another object is to provide a governing system for a turbine including a governor and means for adjusting the governor to select a desired load output, with means for overriding the adjusting means to limit the load to a preselected maximum.

A further object lis to provide a turbine governing system having means for establishing a maximum load limit, with an under-speed release device for removing the limit when the turbine speed drops below a preselected value.

A still further object is to provide a turbine governing system of the type described in which 1 the load limiting device can readily be adjusted during operation, either at the turbine or remotely from a control panel.

Another object is to provide a turbine governing system having a load limiting device with under-speed release means, which is insensitive to vibration and erratic action or bobble of the turbine speed governor, yet is extremely sensitive to changes in turbinespeed.

Other objects and advantages will appear from the following description taken in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic view, partly in section, showing one form which my improved governor system may take, and Fig. 2 is a performance chart illustrating some of the functions of which my system is capable.

As indicated above, governors embodying my invention are especially adapted for controlling a fixed load turbine" driving a generator delivering electrical energy to a network in Yparallel with a number of othersimilar turbo-generators. In such networks it is customary to establish a common speed for all the turbo-generators Vby manually `regulating the speed of one or a few of the units. By thus manually controlling the speed of one turbo-generator, the speed of all the others is xed at the desired value by the electrical characteristics of the network and the generators. This phenomenon, which makes it possible to establish a common speed for all the turbo-generators in a network by manually controlling the speed of one of them, is well known in theart; and the details of the electrical means and theory by which it is brought about are not necessary to an understanding of the present invention. It is suicient to note that the turbine l, in connection with which the present invention is described, is connected to a load device the speed of Which is fixed by extraneous factors. A mechanical analogy would be the case Where a plurality of turbines are directly geared by mechanical means at xed speed ratios to drive a common output shaft, the speed of all the turbines being set to a desired value by manually adjusting the speed of one of them.

For service of the type described, the turbine I is required to operate for long periods of time at Xed speed and fixed load, that is, with the turbine control valve in a substantially fixed position. However, the turbine governor must be capable of immediately taking over control, either in the event of a rise in speed above the established value or in the event of a decrease in speed more than a predetermined amount below the established speed. The devices heretofore used in turbine governors to effect this function have been unsatisfactory because sensitive to vibration and to erratic movement oi the speed governor known as governor bobble. My invention provides a purely hydraulic-mechanical governing system which eiectively performs the desired load limiting function, yet takes over quickly in the event of an abnormal deviation in speed.

Referring now to Fig. 1, my governing system is disclosed as applied to a steam turbine I driving a generator 2 which supplies electrical energy through a circuit breaker 3 to an electrical network 4. From the above discussion, it will be understood that the network 4 interconnects a plurality of similar turbo-generator units la, 2a which are caused to operate at a common speed established by means extraneous to the turbogenerator l, 2, represented diagrammatically as being the manual speed-setting handwheel Ib of turbine la. Motive fluid is supplied to the turbine l through an inlet conduit 5 to the turbine inlet casing 6. The turbine inlet control valve means, represented diagrammatically by the single valve 1, regulates the ilow of motive iiuid to the turbine inlet 8. It will be understood by those familiar with the turbine art that the pressure and temperature of the motive fluid supplied to chamber 6 are maintained substantially constant, while the throttling action produced by valve means 1 produces a variable pressure in chamber 8, the temperature in chamber 8 remaining substantially constant at the value obtaining in chamber 6. It will also be understood that with such an arrangement the output of or load on the turbine is a function of the position of valve means 1.

The valve 1 is positioned by a rod 9 connected to control rod I of a hydraulic servo-motor consisting of a turbine Valve control piston II slidably arranged in a cylinder I2 formed in a housing I3. Piston II is biased downwardly in the valve-closing direction, by a spring I4 arranged in a chamber formed by cylinder l2 on the upper side of piston II, which chamber is drained by means of a conduit I5. Governor operating fluid is admitted to chamber I2 to move piston II upward in the valve opening direction against the bias of spring I4, by pilot valve means described hereinafter.

A suitable speed responsive governor, shown at I5 in Fig. l as a conventional centrifugal fly-ball governor, is arranged to position a rotating pilot valve spindle I1 in a longitudinal direction as a function of the speed of turbine i. It will be understood by those familiar with the art that other speed responsive devices, such as an electrical tachometer generator driven from the turbine shaft with solenoid means for positioning spindle I1 in accordance with the electrical signal from the tachometer generator, might also be used. Spindle I1 is provided with axially spaced cylindrical portions i8 and I9 slidably arranged in the longitudinal bore of a bushing 26. The bushing is likewise slidably arranged in a bore 2I of housing I3, and has axially spaced ports 22 and 23 communicating with annular chambers 24 and 25, respectively, the latter being defined between the outer surface of bushing 20 and the wall of bore 2I. Thebushing 20 is also provided with a third set of ports 26 through which uid may drain through the open lower end of bore 2 I.

Governor motive fluid is supplied from a suitable source past pilot valve means described hereinafter, through conduit 21 to the annular chamber and the communicating ports 23. AS clearly appears from Fig. l of the drawings, the cylindrical portion I9 of spindle I1 is arranged to control the flow of motive fluid from conduit 21 through chamber 25, ports 23, the annular space 28 defined between spindle I1 and the bore of bushing 20, thence through ports 22 to the annular chamber 24 and to conduit 29, which admits the motive fluid to the servo-motor cylinder I2. It will also be seen from the drawing that cylindrical portion I8 of spindle I1 is arranged to drain motive fluid from the servo-motor cylinder I2 through passages 29, 24, 22, and out the drain ports 26.

The lower end of bushing 20 is provided with a fork or yoke section 30 to which is connected a synchronizing and followup lever 3 I, by means of the pivot indicated in dotted lines at 32. It should be noted that spindle I1 passes freely through a central yoke portion 33 of lever 3 I. At one end lever 3| is connected by suitable links 34, 34a to the turbine valve actuating rod I0. This provides a follow-up connection between the servo-motor piston II and the pilot valve spindle I1 in a manner which is well known in the art. The opposite end of lever 3l is connected to a iixed fulcrum 35, carried on a synchronizing screw 36, the position of which can be adjusted by means of a nut 31 arranged to be rotated by any suitable means, such as a gear 38 driven by a synchronizing motor in a manner which will be obvious from the drawing. It will be understood that the synchronizing motor is reversible and may be controlled (by suitable push-button means, not shown) from a remote station, for instance the control panel of the turbine I. It will also be apparent that a suitable hand-wheel (not shown) may be provided on the shaft of the synchronizing motor so that the synchronizing screw 36 may be adjusted manually at the turbine. Screw 36 is provided with suitable stop means in the form of collars 39 and 6i), which dene the no load and full load settings, respectively.

The governor as described thus far is a conventional type which is well known in the art. The turbine l may be started and brought up to running speed by lowering synchronizing screw 36, causing bushing 20 to move downwardly, whereby motive iluid is admitted from conduit 21 through ports 23 past the cylindrical portion I6 to ports 22, thence through conduit 29 to the servo-motor cylinder I2. The pressure of the governor motive fluid in cylinder I2 causes piston II to rise against the bias of spring I4 and open turbine control valve 1. The upward movement of piston rod I0 causes the follow-up links 34, 34a to move lever 3l so as to raise bushing 2U and cause cylindrical spindle portion I3 to interrupt the ilow of motive uid through ports 23, thus halting the upward movement of piston II. When synchronizing screw 3B is moved upwardly toward the no load position, bushing 26 also moves upwardly so that the cylindrical portion I8 uncovers drain ports 26, permitting motive fluid in the servo-motor cylinder I2 to be drained therefrom.

For a given setting of synchronizing screw 36, the speed governor I6 will maintain a corresponding xed position of piston II, in the following manner. If the speed of turbine I increases slightly, the speed governor flyweights inove outwardly thus drawing spindle I1 downward, causing cylinder I8 to uncover ports 26 to drain cylinder I2. This permits piston II to descend slightly until the follow-up linkage 34, 34a restores bushing 20 to a position in which cylinder I8 again blocks the drain ports 25. If turbine speed should decrease slightly, the speed governor flyweights move inwardly causing spindle I1 to move upwardly, whereby the cylinder I3 uncovers the ports 23, admitting motive iiuid from conduit 21 to servo-motor cylinder I2. This causes piston I I to rise until the follow-up linkage restores bushing 20 to the aligned position shown in Fig. l, in which cylinder I9 just blocks ports 23.

My invention adds to the conventional governing means described above additional means for limiting the upward movement of the turbine valve control piston II. This means consists of a second pilot valve arrangement indicated generally at 4I in Fig. l. This second pilot valve means comprises a bushing 42 connected to piston II and slidably arranged in bore 43 in housing I3. Bushing 42 is provided with one or more ports 44 through which governor motive iiuid is admitted from a suitable source (not shown) through conduit 45 to the interior of bushing 42. The bushing is also provided with a second set of ports46 through which governor motive fluid is admitted to'conduit 21, as will be clear rfrom Fig. l. r Slidably arranged in the bore of :bushing 42 is a second pilot valve 41 having cylindrical portions 48 and 49 respectively. will be apparent that spindle 41 and cylinder 43 Aform with the bore of bushing 42 and annular 'chamber to which uid is supplied through ports 44, and from which cylinder 49 permits motive iluid to flow through ports 46 to conduit 21.

Hereinafter this second pilot valve will be referred to as the load limit pilot, since its function is to establish a limiting position beyond which the governor cannot causeA piston II to move, in valve-opening direction.

A plurality of devices are provided for posi-v tioning the load limit pilot 41. The rst means consists of an adjustable stop in the forml of a bellcrank supported on a xed pivot-59 and Y having a rst Varm 5I arranged to engage a stop member 52 secured to a rod 53, which is connected tothe pilot valve 41. The extreme end of rod 53 is provided with a flange 54 and a coil spring 55 arrangedv between flange 54 and the upper surface of bellcrank arm 5I. This arrangement permits rod 53 to move downwardly,

regardless of the position of the adjustable stop 5I, while the upward movement of rod y53 isl klongitudinally in suitable keyways in the bore of bushing 59.

Screw 51 carries a nut 62 which does not rotate but travels longitudinally on screw `51 as the latter is turned. The position of nut 62 is ordinarily xed by mechanical latching means including links 63, 64, the latter of which is arranged to be engaged by a latch member 65. Latch member 65 has an end portion engaged by a tripping rod 66, and a second cam-shaped end 81 arranged to be engaged bythe nut 62 for resetting latch 65, as described below. Nut 62 is biased to the right by means of a coil spring 63 arranged between the end of the nut and the adjacent end of bushing 56. Movement of screw 51 to the right is limited by the movement of a collar 69 to the dotted line position shown at 69a in Fig. 1.

With nut 62 held xed by the linkage 63, 64

l and the latch 65, it will be apparent that screw 51 may be adjusted longitudinally by rotating hand-wheel 69, so that the bellcrank 5I, 56 may be positioned anywhere from the no load position, indicated by dot-dash lines 19 lto the full load position, indicated by the dot-dash lines 1I.

The emergency over-speed governor, indicated diagrammatically at 12 in Fig. 1, is vdriven from the turbine shaft and is arranged` to engage a latch lever 13 when turbine speed reaches the value for which the emergency governor is It will be understood by those skilled in set. the art that this emergency governory is a slightly unbalanced centrifugal device which moves to an eccentric position under emergency over-speed'conditions, as indicated by the dotted l; circle 14 in Fig. v1. Such movement causes latch 13 to move counterclockwise, thus releasing spinvldle15 whichis then biased downwardly by a "coil spring 16 so as to move trip rod 66 downwardly to unlatch member 65 from the link 64.

-When link 64 is thus freed, biasing spring 56 causes the nut 62to move to the right, the

keys 6I sliding. freely in the bushing 59 untilcollar 69 reaches its limiting position 69a, with link 64 in the dot-dash position 64a. This movement of screw 51 causesbell-crank I5I, 56 to move to the no load position 10, and this in turn causes the rod 53 to be moved downwardly.

The action of the load limit pilot 4| will now be noted. It will be apparent that as the pilot valve-41 moves downwardly from the position shown in Fig. l, cylinder 49 progressively blocks the ports 46 until nally the supply of motive uid from conduit 45 to conduit 21 is interrupted movement of ro altogether. When this happens, the speed governor I6 and the rst pilot valve I1 are no longer capable of moving piston II in the valveopening position. The manner in which pilot vvalve 41 acts to limit the upward movement of piston it will now be apparent. As piston II moves upwardly, for instance under the control of governor I6 and synchronizing screw 36, bushing 42 likewise moves, until the ports 46 are entirely blocked by cylinder 49. The upward movement of piston II is therefore stopped, because cylinder 49 interrupts the flow of motive iiuid to the first pilot valve I1. As will be understood by those skilled in the art, there is an appreciable amount of leakage between the respective cylinder members I8, I9, bushing 26, and the bore 2l. By reason of this leakage, biasing spring I4 will cause piston II to start downwardly as soon as cylinder 49 interrupts :ne supply of motive uid to conduit 21 and the first pilot valve. This downward creepage of piston II causes the ports 46 in bushing 42 to be slightly uncovered by cylinder 49 whereby motive fluid is again supplied through conduit 21 to the rst pilot valve, which may then admit motive fluid to the chamber I2 to restore piston II to the position in which cylinder 49 is just aligned with the ports 46. It will therefore be seen that the load-limit pilot 41 establishes a limiting position beyond which governor I6 cannot cause piston I I to move in the valve-opening direction.

Control rod 53 may be moved downwardly, either by actuating hand-wheel 66'to move stop 6I toward the no load position 10, or by reason of disengagement of the latch means 64, under the inuence of emergency speed governor 12. Such downward movement of rod 53 and the pilot 41 promptly causes cylinder 46 to block the passages 46, shutting off the supply of motive uid to the first pilot valve as noted above, whereupon piston Il creeps downwardly by reason of the leakage mentioned above. If the downward 53 continues, the downward creepage of piston il will not cause cylinder 49 to uncover ports 46, and therefore the downward vcompany it. way to the no load position 16, pilot 41 causes creepage continues. The result is that when pilot 41 moves downwardly, piston ll is caused to ac- When stop member 5I moves all the ranged to engage the upper surface of flange 54,

and a second arm 19 connected to the endvof` a longitudinally movable screw 80. Screw 80 is arranged to slide longitudinally in a support housing 8|, and is arranged to be rotated in either direction by means of a bushing 82 having internal keyways or splines engaging keys 83 on the right-hand end of screw 80. Bushing 82 may be rotated manually, at the turbine, by means of a hand-wheel 84. It may also be remotely adjusted, from the turbine control panel, by means of the load limit motor 85 which has suitable circuits with push-button control (not shown). As will be apparent from Fig. l, the motor 85 is geared to bushing 82 by means of a friction coupling including a friction disk 86 biased against the side of gear 81 by a suitable coil spring 88. This arrangement permits screw 80 to be rotated by f hand-wheel 84, with the friction coupling slipping and gear 81 remaining stationary.

Carried on the screw 80 is a nut 89 arranged to normally be held fixed by latch means including links 90 and 9|, the latter of which is adapted to be engaged by a latch 92. Member 92 has a projecting tripping arm 93 engaged by coil spring 93a which biases latch 92 into latching engagement with link 9i, and also causes the tripping arm 93 to remain engaged with the projecting end of piston rod 94 of a hydraulic servo-motor 95, the function of which will b-e seen hereinafter.

It will be apparent from Fig. 1 that as long as latch 92 holds nut 89 iixed, the screw 80 can be adjusted longitudinally by proper rotation of screw 80, either by handwheel 84 or the load limit motor 85. It will also be apparent that such longitudinal movement of screw 80 will cause bellcrank 18, 19 to be appropriately positioned between the full load position, shown in full lines in Fig. l, and the no load position" indicated by the dot-dash lines 96. As screw 80 is retracted by its rotation in nut 89 from the position represented in Fig. 1, arm 'I8 of the bellcrank lever will descend until it engages flange 54. Further movement of screw B to the right will cause arm 18 to move rod 53 downwardly, stop member 52 meanwhile moving downwardly away from the primary stop lever 5I. It will be seen that screw 80 and the devices associated with it constitute secondary` means for positioning rod 53 in the range below the upper limiting position established by the engagement of member 52 with stop lever 5|. Thus the maximum position to which piston I I can be moved in valve-opening direction by speed governor I6 and the synchronizing screw 3E may be limited by the screw 51 acting independently of screw 80, or by the screw 80 acting to position rod 53 in the range below the limiting position established by the stop lever 5 I. In other words, screw 51 and its associated devices constitute means for establishing a primary or absolute maximum limit beyond which piston |I -cannot be moved in the valve-opening direction.

On the other hand, screw 80 and its associated devices constitute means for establishing a secondary limit, within the range below the absolute limit established by screw 51.

Associated with the screw 80 are under-speed release means arranged to render ineffective the secondary load limiting device when the turbine speed decreases below a preselected value. This under-speed release mechanism comprises the servo-motor 95, including a piston 91 longitudinally slidable in a cylinder formed in the housing 8 I. Piston 9'I is biased to the left by a coil spring 91a and is adapted to be moved to the right by fluid pressure communicated to piston 91 through conduit 98. It will be apparent from Fig. 1 that movement of piston 91 causes the piston rod 94 to engage trip arm 93 so as to disengage latch 92 from link 9 I, permitting coil spring 99 to bias nut 89 and screw 80 to the left, link 9| thereby being moved to the dot-dash position 9 Ia. Engagement of the collar |00 with housing 8 I, as shown in Fig. l, determines the extreme position or full load position of the screw 80.

In order to reset the secondary load limit device so that nut 89 is again secured by latch 92, the procedure is as follows. Screw is rotated so that nut 89 moves to the right, collar |00 still engaging housing 8|. As nut 89 moves to the right, the end of link 9| rides up the inclined cam edge IOI of latch 92. thus causing the latch to be rotated counterclockwise against the bias of spring 93a, until the end of link 9| snaps into the position shown in Fig. 1. Spring 94 will then cause latch 92 to secure link 9| until tripped by action of servo-motor 95.

The supply of motive fluid through conduit 98 to servo-motor 95 is controlled by a third pilot valve indicated generally at |02 in Fig. 1. This under-speed release pilot is arranged to be positioned by the turbine speed governor I0, and may be conveniently associated directly with the first pilot II. As shown in Fig. 1, the underspeed release pilot |02 includes a spindle |03 formed as a continuation of the rst pilot spindle I1 and having a cylindrical portion |04. The pilot |03. |04 is slidably arranged in a bore |05 formed in a bushing |06 which is separate from bushing 20 and axially adjustable in the bore 2| by means of a thread engaged by an adjusting nut |01, which may be secured to housing I3 by one or more suitable threaded fastenings |08. It will be apparent that the position of bushing |06 may be adjusted longitudinally relative to bore 2| by removing the threaded fastening |08, rotating nut |01 to a desired position, and reassembling the fastening |08.

The bushing |06 is provided with a first set of ports |09 arranged to receive motive fluid from conduit 45 by way of the annular space I|0 and conduit III formed in housingl I3. The chamber defined by bore |05 above cylinder |04 is drained by means of a passage |I2 in bushing |06. It will be apparent from Fig. 1 that iluid collecting in the upper portion of bore 2 I, above bushing 20, will be drained through the passage II3. It will also be seen that the upper end of spindle I1 forms an annular shoulder ||4 arranged to cooperate with the adjacent end of bore |05. When shoulder II4 is in the position shown in Fig. 1, forming a clearance space ||5 with the adjacent end of bushing |06, servomotor 95 is drained of fluid through conduit 98, the annular space I6 surrounding pilot rod |03, and the clearance space II5.

The position of the rst pilot I'I, I8, I9 shown in Fig. 1 represents the condition when the speed is normal and the speed governor I6 and synchronizing screw 36 are in control of the speed and load. If now the speed should drop below the established speed, then spindle I1 will rise until iinally shoulder ||4 closes completely the clearance space II5, and simultaneously cylinder |04 uncovers port |09, whereupon motive fluid from conduit 45 will flow through conduit III, port |09, the annular space IIB, thence to conduit 98 and servo-motor 95. Piston 96 is thereby moved to the right against the bias of spring 91a, causing latch 92 to disengage link 9|, with the result that nut 89 and screw 8@ are biased quickly to the full load position by spring 9s. It will be apparent that the size of the clearance space II determines the amount the turbine speed must drop below the established speed before servo-motor 95 is actuated. It will also be apparent from Fig. 1 that this critical speed drop required to actuate servo-motor Q5 can be adjusted by properly positioning bushing |06 by means of the adjusting nut |01.

The functions which my improved turbine governing system is capable of performing will be seen from the following examples. The operation of the system will be described in connection with the performance curves of Fig. 2, in which the abscissa represents the turbine load or output, in per cent of rated load, while the ordinate represents turbine speed, expressed in per cent of rated speed.

With the primary load limit screw 51 retracted and the secondary load limit screw 89 extended to their respective full load positions, it is possible to open valve 1 and bring turbine I up to the normal speed by means of the synchronizing screw 36 and the operation of the speed governor I6, in the manner used with conventional turbine governors. This is accomplished simply by rotating screw 3S from the no load position to a desired setting corresponding to the load and speed desired. During such operation, the load limit pilot valve 4? is in its uppermost or full load position and operating iluid from conduit 45 is permitted to pass to the speed control pilot I1 without interference from 'the load limit pilot.

Alternately, the turbine may be started and brought up to speed by means of the primary load limit screw El. In order to accomplish this the latch 64, 65 must be reset, if the turbine was previously stopped by tripping action of the emergency over-speed governor 14. This resetting operation is accomplished by rotating hand-wheel 6E), collar 69 being in its dotted line position 69a, so as to move nut 62 to the left, link Ell moving from the dot-dash position 54a toward the position shown in full lines. Movement of nut S2 is continued until it engages the end portion 61 of latch member 65. Further movement of nut 62 against the end portion G1 will cause latch 65 to rotate counterclockwise so as to engage the end of link B4. Counterclcckwise movement of latch 65 will of course raise tripping rod 56 against the bias of spring 16 and cause lever 13 to drop counterclockwise so as to engage the end portion of rod t5. The over-speed emergency trip is thereby reset to the position shown in full lines in Fig. l. Hand-wheel 60` can then be rotated to retract screw 51 to the left, collar 69 being thereby drawn from its dotted line position 53a and bellcrank 5I, 5S being rotated counterclockwise so as to raise control rod` 53. This motion causes piston II to follow the pilot 41 upwardly, by reason of the supply of governor motive fluid from conduit 45 past pilot l? through the speed control pilot I1, I3, I9 to cylinder I2. When piston II rises to a position corresponding to the turbine load for whichk synchronizing screw 365 is set, pilot I1 will bring cylinders I3, iii into aligned position with ports 23 respectively, as shown in Fig. l, whereupon the speed governor I5 takes over control and prevents a further rise of piston II. Further upward motion of. rod53 merely raises pilot 41 so as to provide free communication between conduits 45 and 21. With the turbine thus brought to the desired speed and load, determined by the position of synchronizing screw 36, the generator 2 is connected to the network 4, as by closing circuit breaker 3. Thereafter the speed of turbo-generator I, 2 will be established by reason of its interconnection with the other turbo-generators connected to network 4, as described above.

Assuming that the synchronizing screw 36 was set to its half load position, substantially that represented in Fig. l, then the speed governor it will tend to control the turbine in accordance with the curve an in Fig. 2. This curve will be recognized by those skilled in the art as the speed regulation curve, representing the change in speed of the turbine from full load to no load when controlled by the speed governor I6. However, since the speed of turbine I is being held xed (at per cent of rated speed) by reason of its interconnection with the turbogenerator Ict, 2a, the governor I 5 will always rotate at this established speed, and the action of the governor Iwill be to hold the turbine load xed at the point p in Fig. 2. It will be seen that the point p corresponds to 100 per cent speed (fixed by the interconnection of turbo-generator I, 2 with unit Ia, 2a in the network 4) and 50 per cent load (determined by the half load setting of synchronizing screw 36). If the synchronizing screw 36 were set to its full load position, then the governor would try to follow the curve my, but would be limited to operation at the point y by reason of the interconnection with other turbo-generators, point y representing 100 per cent load at 100 per cent of the yestablished speed.

Now, assuming that synchronizing screw 36 is set at half load s-o that the governor will tend to follow curve cm as described above, the primary load limit screw 51 may be moved to the right so as to rotate bellcrank 5I, 56 clockwise and lower pilot 41. When pilot 41 gets to its half load position, cylinder 43 will be just aligned with the ports 46. In this condition, neither the synchronizing screw 35 nor the governor i5 can cause piston II to move above its hahc load position. If now rod 53 is lowered still further so that pilot 41 goes below the half load position, then piston II will follow pilot 41 downwardly, as described above. Conversely as pilot 41 rises, piston II will follow it upwardly until, when the half load position is reached, cylinder 43 again becomes just aligned with ports 46. When pilot 41 moves above this half load position, ports 46 are no longer blocked by cylinde-r 4i? and pilot I1 takes over control in accordance with the operation of governor IS.

Assume now that the primary load limit screw 51 is set by means of hand-wheel Ell to the position corresponding to three-fourths load, approximately that shown in full lines in Fig. l. Governor it will now control pilot I1 to position piston I! in accordance with the setting of synchronizing screw 3S. The primary load limiting device now serves only to establish threefourths load as the absolute limit above which synchronizing screw i5 will be ineffective to position piston Ii. Thus it will be seen that the primary limiting screw 5l provides means for setting manually, at the turbine by means of hand-wheel Gt, a limiting load which may not be exceeded by controlling synchronizing screw 35 remotely from thel turbine control panel.

Thus, a remote operator at the turbine control panel is prevented from inadvertently adjusting screw 35 to call for a load above the preselected desired maximum. Setting the primary load limit device to a position corresponding to threefourths load has the effect of establishing 4the line cd in Fig. 2 as an upper limit, so that governor IS and synchronizing screw 36 are able to exercise control only in the area to the left of line cd.

Now with synchronizing screw 36 set at half load and the primary load limit screw 51 set at three-fourths load, the secondary load limit screw 80 may be adjusted. It is rst necessary to adjust bushing |06 so that the clearance ||5 corresponds appropriately to the maximum speed drop to be permitted. It may be assumed that the under-speed release pilot |02 is adjusted so that servo-motor 95 will be actuated if the turbine speed decreases one per cent, that is, to 99 per cent of the established value. The effect of thus adjusting the under-speed release pilot |02 is to establish the line ti in Fig. 2 as the minimum value below which turbine speed will not fall.

Now, assuming that latch 9|, 92 has been reset to the position indicated in Fig. 1, by the method described above, the secondary load limit screw 80 can be adjusted, by means of hand-wheel 84 at the turbine or remotely from the control panel by means of load limit motor 85. As screw 80 is retracted from the position shown in Fig. 1, bellcrank 13, 19 rotates counterclockwise until the arm 10 just engages collar 54 when screw 30 is set to the three-fourths load position (the limiting value established by screw 51). If now screw 83 is moved below the three-fourths position, then rod 53 is moved downwardly by the engagement of lever 18 with collar 54, with the result that stop member 52 moves away from the primary stop lever The secondary load limiting screw 89 now determines the maximum load beyond which piston cannot rise. If screw 89 is set to the half load position, then cylinder 49 of the load limit pilot 41 again becomes aligned with ports 45, and upon further retraction of screw 80 causing downward movement of pilot 41 below this point screw 80 takes control of the system away from governor l0 and the synchronizing screw 36 (which is calling for half load operation).

Assume now that the secondary load limit screw 89 is set to the 2O per cent load position. This has the effect of establishing the line sf in Fig. 2 as the limit above which the turbine may not operate. In this condition, the synchronizing screw 3S (set at half load position) prevents operation above the line ar in Fig. 2; and the secondary load limit screw 80 restricts operation to the left of the line sf. Ii now, due to some abnormal operating condition such as a disturbance somewhere in the network 4, the normal speed which is established for the entire network varies so that the speed of turbine drops from 100 per cent to 991/2 per cent (from point lc to o in Fig. 2), the speed governor I6 will raise the pilot l1 in an attempt to admit motive fluid to cylinder l2 and raise piston so as to open valve 1 and restore the speed to 100 per cent. However, this action is prevented because the cylinder 49 of pilot 41 blocks ports 4S to interrupt the flow of motive fluid through conduit 21 to the pilot I1, |8, I9. If now the speed drops still further, for instance to 99 per cent represented by point h in Fig. 2, then governor IB raises pilot |1 and the under-speed release pilot |03 sufficiently that cylinder |04 permits fluid to flow from conduit I into conduit 98 to actuate servomotor 95. Latch 9|, 92 is hereby disengaged and spring 99 moves nut 89 and screw 80 to the extreme left or full load" position shown in Fig. l. This has the eiect of removing the limiting line sf in Fig. 2. Upward movement of the lever 18 permits rod 53 to rise until member 52 engages stop lever 5|. Thus pilot 41 is restored to the three-fourths load position, so that the line cd in Fig. 2 again becomes the limit above which the turbine will not operate. However, piston will follow pilot 41 upwardly only until it reaches the half load position. This increase in load is represented by the line hm in Fig. 2. At point m, which is approximately at '12 per cent rated load, the speed governor IB resumes control since the synchronizing screw 35 is set to call for operation along the line an. Thus it will be seen that as long as the speed established in the network is at the subnormal value of 99 per cent, turbine will operate at 72 per cent of its rated load, although synchronizing screw 36 is set to call for half load (at 100 per cent rated speed). If now the established speed in the network rises to 100 per cent of the normal value, then governor I6 will cause the turbine operation to follow the line from m to p along the half load curve an.

Now if, with synchronizing screws 39 set at half load, the primary load limit screw 51 set at three-fourths load, and the secondary load limit screw S0 set at 20 per cent as before, the established speed in the network 4 should suddenly drop to 98 per cent of the normal value, the operation of turbine would follow the line from le to s in Fig. 2. When the point h is reached, the under-speed release pilot |02 will energize servo-motor 95 as before and trip the secondary limit screw to its full load position. Pilot 41 is thus permitted to rise to the three-fourths load position determined by lever 5|, the turbine operation following the line s to c in Fig. 2. It should be noted that without the primary limit 5| set at three-fourths load so as to establish the line cd as an upper limit, the load on turbine woud have increased along the curve sc and to the point n on the half load curve om. Since point n represents 92 per cent of rated load, it may be undesirable to cause the load on turbine to suddenly increase to such a high value. Therefore, the primary load limit screw 51 serves to prevent the load rising above the predetermined maximum. If now the established network speed rises, the operation of turbine will follow the line c to b. At point b the governor I6 takes over and the operation of the turbine will follow the line bmp, as dictated by the half load setting of synchronizing screw 36.

It will be Seen from the above that with the synchronizing screw 36, primary load limit screw 51, and secondary load limit screw 80 adjusted as described above, the area dened by the lines arht in Fig. 2 represents the zone in which the turbine can operate without causing any components of the governing system to act. If operation tends to pass into the area above line ar, then governor I5 will lower 'piston so that operation returns to the linear. The secondary load limit screw 30 establishes the upper limit line rh; and if the operation drops below the line th, then the under-speed release mechanism acts to remove the line .sf as the upper limit and 'I3 frees the turbine to operate anywhere' within the area ar'pmht. f

It willbe apparent that itis not necessary. to use the primary load limit screw' 51 to establish the limit cd. -Bellcranl'ai- 5i, V5t maybe left in its full load position so thatcontrol will be eiected by the secondary' loadv u'mi-t screw 80 and the governor I6, asset by the synchronizing screw 35. The primary load limit screw' 5T will act only in Starting up or shutting down the turbine yby means of hand-.wheel B6, orv inl the event that emergency speed governor l2 trips the latchn, 65.k Furthermore, instead Aof being' positioned only by the hand-wheel klill, the primary stop 5I may be arranged to be positioned automatically by other means responsive to some' operating condition of the powerplant, `for `in stance the boiler pressure.- n

From the above examples it will be seen that my invention provides an improved turbine governing system having a plurality of load limiting devices, one of which establishes a primary limiting load which may not be exceeded and another which establishes asecondar'y lim-it below the primary'limit, with under-speed release mechanism for removing the secondary limit in the event that thetur'bine speed drops more than' a preselected amount.

What I claim as new and desire to lsecure by Letters Patent of the United States is:

l. In a governing system for a prime mover powerplant having inlet valve means, the combination of a source of governor operating fluid under pressure, motor means for regulating the inlet valve means including a cylinder with a piston' for positioning said valve means and first pilot valve means for controliingthe flow Vof'op*n erating' fluid from said source tothe cylinder, governor' means responsive to prime-mover speed for positioning the first pilot valve, first adjustable means for limitingmovement of the piston in valve-opening direction to a first preselected value, second adjustable means for limiting movement of the piston in valve-opening direction to a second preselected value smaller than said first limiting value, and underespeed release' means associated with the speed governor for rendering ineffective said second adjustable means to restore control of the system to the speed governor aslimited by the rst adjustable means when the speed decreases from normal to a preselected minimum value.

2. In a governing system for a prime mover povverplant unit having inlet valve means, the combination of a source of governor operating fluid unde-r pressure, motor' means forviegulating' the inlet valve including a cylinder with a piston for positioning said valve and rst pilot valve' means for controlling the flow of operating fluid from said source to the cylinder, governor means responsive to prime mover speed for positioning the first pilot valve, means for limiting movement of the piston in valve-'opening direction to a preselected position `comprising second pilot valvel associated with the speed governor for rendering v ineffective the adjustable means to 'restore con-i trol of the system to the speed governor 'when 'the speeddecreases from normal to a preselected minimum value;

o 3, In a governing system for a prime mover Qfpoiverplant unit having inlet valve means, the combination of a source of governor operating fluid under pressure, motor means ior regulating the inlet valve means including a cylinder with a piston for positioning said'valve means andfirst l pilot valve means for controlling the flow of operating fluid from said source to the cylinder, Vgovernor means responsive to prime mover speed for positioning the rst pilot valve, means for limiting movement of the piston in valve-opening vdirection to a plurality of preselected positions VV"comprising second pilot Valve means associated r`with the piston and arranged to interrupt the now of operating fluid to the rst pilot valve when the piston reaches said preselected limiting position, first adjustable stop means for limiting' movement of the second pilot Valve to a ,first pre selected position, second adjustable means for moving the second pilot valve to any position Within the range of movement below the limiting j: position established by said first stop means, and under-speed release means associated. with the speed governor for rendering ineffective said sec'- ond' adjustable means to restore the system to control by the speed governor as limited by said rst adjustable stop means when the speed decreases from normal to a preselected minimum value;

v 4', In a governing system for a prime mover powerplant unit having inlet valve means, the

vcombination of a source of governor operating second pilot valve means associated wi fluid under pressure, motor means for regulating the inlet valve including a cylinder with a piston for positioning said valve first pilot valve 'means for controlling the now of operating fluid 'j from said source to the cylinder', govern i "cans responsive to prime mover speed for po ning the first pilot valve, means for limiting move-- ment of the piston in valve-opening direction to a plurality of preselected positions MN "icing e oiston and arranged to interrupt the of operating uid to the first pilot valve when the pi n reaches said preselected limiting position, si, adjustable stop means for limiting movement of the second pilot valve to a rst preselected position, second adjustable means for moving the speed governor as' limited by 'the iirst adjustable stop means, and third pilot; valve means posi- ,tione'd by the speed governor for controlling said operating fluid to aetuate said servo-motor when the speed decreases from normal to a preselected mini-mum value.

In a governing system for a prime mover powerplant unit having inlet valve means, the combination of a source of governor operating fluid under pressure, motor means for regulating the inlet valve means including a cylinder with a piston for positioning said valve means and a y,pilot valve for controlling the flow of fluid from said source to the cylinder, governor means responsive to prime mover speed Jfor posit' pilot valve. means for limv @ning the g the movement the piston in valve-opening direction to a desired maximum value, and under-speed release means associated `with the speed governor for endering ineffective said limit means when the speed decreases from normal to a preselected minimum value.

6. In a governing system for prime mover powerplant unit having inlet valve means, the combination oi a source of governor operating fluid under pressure, motor means for regulating the inlet valve including a cylinder .viih piston lor positioning said valve and pilot valve means for controlling the flow of fluid lrcm said source to the cylinder, governor means responsive to prime mover speed for positioning the pilot valve, adjustable means for limiting the movement ci the piston in valve-opening direction to a desired maximum value, said adjustable means including second pilot valve means associated with the pioton and arranged to stop the now of operatingr fluid from the source to the -rst-mentioned pilot valve when the piston moves to said'limit-ing position, and under-speed release means associated with the speed governor for rendering ineiective said adjustable means when the speed decreases irom normal to a preselected minimum value.

7. In a governing system for a prime mover powerplant unit having inlet valve means, the combination of a source of governor operating iiuid under pressure, motor means for regulating the inlet valve including a cylinder with a piston for positioning said valve and pilot valve means for controlling the flow of fluid from said source to the cylinder, governor means responsive to prime mover speed for positioning the pilot valve, adjustable means for limiting the movement of the piston in valve-opening direction to a desired maximum value, said adjustable means including second pilot valve means associated with the piston and arranged to stop the flow of operating uid from the source to the first mentioned pilot valve when the piston moves to said limiting posi tion, and under-speed release means for rendering ineffective said adjustable means, including a servo-motor with third pilot valve means positioned by the speed governor and arranged to control the flow of said operating iiuid to actuate the servo-motor when the speed decreases from normal to a preselected minimum value.

8. In a governing system for a prime mover powerplant unit having inlet valve means and adapted to operate at a preselected normal speed, the combination of a control member for regulating the inlet valve means, governing means adapted to control the position of the control member to maintain prime mover speed at the preselected normal value, synchronizing means for adjusting the governing means to change the normal position of the control member, adjustable stop means for preventing movement of the control member in valve-opening direction beyond a preselected limiting position, and underspeed release means controlled by the governing means for rendering ineffective said stop means whereby the system is restored to unrestricted control by the speed governor when the speed decreases below the normal speed to a preselected minimum value.

9. In a governing system for a prime mover powerplant unit having inlet valve means and adapted to operate at a preselected normal speed, the combination of a control member for regulating the inlet valve means, governing means adapted to control the position of the control member to maintain prime mover speed at the preselected normal value, synchronizing means for adjusting the governing means to change the normal position of the control member, adjustable stop means for preventing movement of the control member in valve-opening vdirection beyond a preselected limiting position, and under-speed release means including a servo-motor for rendering ineffective said stop means, and pilot means associated With the governing means for controlling the ilow ol? said operating uid to actuate sald servo-motor when the speed decreases below the normal speed to a preselected minimum value whereby the system is restored to unrestricted control by the governing and synchronizing means.

10. In a governing system for a prime mover povverplant unit having inlet valve means and adapted to operate at a preselected normal speed, the combination of a control member for regulating the inlet valve means, governing means adapted to control the position of the control member to maintain prime mover speed at the preselected normal value, synchronizing means for adjusting the governing means to change the normal position of the control member, first adjustable stop means for establishing a primary limiting position beyond which the governing and synchronizing means cannot cause the control member to move in the valve-opening direction, second adjustable means for establishing a secondary limiting position within the range below said primary limiting position and under-speed release means controlled by the governing means for rendering ineiective the second adjustable means when speed drops below normal to a preselected minimum value whereby the system is restored to control by the governing and synchronizingmeans as limited by the nrst adjustable stop means.

11. In a lgoverning system for a prime mover having motive fluid inlet control means, the combination of a hydraulic motor with a piston for actuating the inlet control means, a source of governor operating fluid under pressure, a iirst pilot valve-for directing motive fluid from said source to the motor, means responsive to prime mover speed for positioning the first pilot valve, a second pilot valve associated With said piston and adapted to interrupt the supply of motive fluid to the first pilot valve when the piston is in a position corresponding to a preselected condition ofthe inlet control means, and means for positioning the second pilot valve to determine the limiting position to which the rst pilot valve can cause said piston to move.

l2. In a governing system for a pri-me mover having motive fluid inlet control means, the combination of a hydraulic `motor with a piston for actuating the inlet control means, a source or' governor operating fluid under pressure, a iirst pilot valve for directing motive fluid from said source to the motor, means responsive to prime mover speed for positioning the iirst pilot valve, a second pilot valve associated With said piston and adapted to interrupt the supply of motive iiuid to the first pilot valve when the piston is in a position corresponding to a preselected condition of the inlet control means, and means for positioning the second pilot valve to determine the limiting position to which the iirst pilot valve can cause said piston to move, said last-named positioning means including means for manually moving the second pilot valve to any desired position in its range of movement, and means including an emergency over-speed governor for moving the second pilot valve to a preselected emergency position regardless of the position of said manual means.

13. In a governing system for a prime mover having motive fiuid inlet control means, the

combination of a hydraulic motor with a piston for actuating the inlet control means, a source of governor operating fluid under pressure, a rst pilot valve for directing motive iiuicl from said source to the motor, means responsive to prime mover speed for positioning the first pilot valve, a second pilot valve associated with said piston and adapted to stop the supply of motive fluid to the first pilot valve when the piston is in a position corresponding to a preselected condition of the inlet control means, and means for positioning the second pilot valve to determine the limiting position to which the rst pilot valve can cause said piston to move, said last-named positioning means including means for manually moving the second pilot valve to any desired position in its range of movement, means including an emergency overspeed governor for moving the second pilot valve to a preselected emergency position regardless of the position of said manual means, second means for manually moving the second pilot valve to any position below the upper limit determined by the first-mentioned manual means, and servo-motor means responsive to an operating condition in the powerplant for rendering ineffective said second manual means.

14. In a governing system for a prime mover powerplant unit having motive fluid inlet control means, the combination of a hydraulic motor With a piston for actuating the inlet control means, a source of governor operating fluid under pressure, a first pilot valve for directing motive fluid from said source to the motor, means responsive to prime mover speed for positioning the first pilot valve, a second pilot Valve associated with said piston and adapted to interrupt the supply of motive fluid to the rst pilot valve when the piston is in a position corresponding to a preselected condition of the inlet control means, and means for positioning the second pilot valve to determine the limiting position to which the first pilot valve can cause said piston to move, said last-named positioning means including means for manually moving the second pilot valve to any desired position in its range of movement, means including an emergency over-speed governor for moving the second pilot valve to a preselected emergency position regardless of the position of said manual means, second means for manually moving the second pilot valve to any position beloW the upper limit determined by the first-mentioned manual means, servo-motor means for rendering ineffective said second manual means, and means associated With said speed responsive means for actuating the servo-motor when the speed drops below a preselected minimum value.

RAYMOND SHEPPARD.

REFERENCES CITED The following references are of record'in the file of this patent:

UNlTED STATES PATENTS Number Name Date 1,204,564 Grun Nov. 14, 1916 1,444,437 Ver Planck Feb. 6, 1923 

